Solved: I-95`s South Fork Puzzle

Anyone who drives on Interstate 95 knows how it goes. Traffic on the bridge inexplicably slows to a crawl, and you think: ``Accident ahead. Must be a big one.``

Now, considering there are about 50 accidents a month on I-95 between Davie Boulevard and the Fort Lauderdale-Hollywood International Airport -- more than on any other segment of the interstate -- that`s only a logical assumption.

But it`s wrong.

For, upon reaching the crest, you look down the other slope and find . . .

What . . .?

No flashing lights. No sirens. No red flares. No accident. Just cars.

Why, then, the slowdown?

Engineers and police officers will point to the steepness of the bridge and the volume of traffic in that area.

``The big problem with the South Fork bridge is that there are too many cars and not enough road,`` said Lt. Rich Rossman of the Florida Highway Patrol.

Rossman said Griffin Road to Oakland Park is the most congested stretch of I- 95, and State Road 84 is probably the busiest east-west thoroughare in the county. Traffic from the airport, Port Everglades and Fort Lauderdale all enter the interstate from SR 84.

Rossman said the problem is compounded by the high number of large trucks coming out of Port Everglades.

``These big old tankers come down the ramp, get on I-95 and immediately try to climb that bridge,`` he said. ``Forget it. They slow down everyone behind them.``

The slowdown is not only unnerving, it`s downright dangerous.

``That area probably has the highest frequency of accidents on the interstate,`` Rossman said.

In December alone, the FHP investigated 76 accidents, with the rear-end collision far and away the most common type.

``They follow each other too close, they don`t look where they are going and then they turn their heads to look at something,`` Rossman said. ``We get a lot of chain reaction-type of accidents with three, four, five cars.``

And, with the interstate sitting next to the main runway of the airport, too often the thing being watched is a wide-bodied 747 coming in for a landing.

``That is a problem,`` Rossman said. ``Periodically, we even have people who stop to watch the airplanes.``

Florida law stipulates that drivers cannot stop on an expressway except for an emergency. Violators are subject to a $25 ticket.

Those are the most likely reasons. But others will tell you that to solve the Mystery of the South Fork Bridge, you need only peer into the subconscious mind of the Gold Coast driver.

One view comes from Dr. Nate Azrin, director of the Nova University Psychological Clinic. He said the slowdown only proves the principle of stimulus generalization.

The principle, proven by pillars of psychology such as Ivan P. Pavlov and B.F. Skinner, says that the behavior of man -- and animal -- is determined to some extent on repeated patterns of stimuli.

Pavlov, whose research in the field won him a Nobel Prize, called it the conditioned reflex. Alter the stimulus, and the behavior will change in direct proportion.

``Whenever you change the stimulus or conditions in which the behavior -- like driving -- has been learned, the performance will be different,`` Azrin said.

``When the individual encounters a strange configuration like a hill, there is an emotional reaction. The driver might be expected to change his driving habits.``

Simply put, drivers accustomed to the tropical lowlands of South Florida don`t know or have forgotten how to drive on hills. When they encounter one, they react strangely.

The plain fact is that the bridge over South Fork is too steep for the Gold Coast driver.

It has a 4 percent grade, which means that it rises four feet every 100 feet of road. Most bridges in South Florida have no more than a 3 percent grade. The steeper the grade, the more gravity pulls your car.

While a 1 percent difference might not seem like much, engineers working for the state Department of Transportation estimate that it is enough to cause cars on the South Fork Bridge to go 10 mph slower than on other bridges.

``There are limits as to how steep you can make a vertical grade,`` said Mike Sherman, a spokesman for two major engineering firms that work in tandem for the state Department of Transportation. ``If a grade is too steep, you can`t see far enough to be comfortable. So what do you do? You slow down.``

To compound the problem, that section of Interstate 95 is just not enough road for all that traffic.

Sherman said the heavy injection of traffic from Davie Boulevard and State Road 84 is like ``trying to get 12 pounds into an eight-pound space.``

``The ramps from Davie Boulevard southbound and State Road 84 northbound are, in effect, introducing a fourth lane of traffic onto what is otherwise a three-lane road,`` he said.